1. Field of the Invention
The present invention relates to a mold in which an organic or mineral material is shaped by application of known techniques such as blowing, pressing or reactive injection, the mold being cold or alternatively equipped with a heating means as the case may be. Different techniques among those cited hereinabove are frequently used in combination.
2. Discussion of the Background
The problem that in particular motivated the in-depth studies carried out by the inventors is that of release from the mold, in the case of articles with special shapes comprising square or rectangular cross sections or more complex geometries. In fact, when an article with rectangular cross section is produced in a classical two-jaw mold with a mold joint plane cutting, for example, the rectangular cross section of the internal mold cavity into two equal parts parallel to two sides of the rectangle, the normal method of release from the mold by opening the mold by rotation of the jaws around an axis perpendicular to the said section and included in the joint plane is precluded: such release from the mold would cause the molded substance to be gripped by the material constituting the walls of the internal cavity, in the zone of the two apices of the rectangular section most distant from the axis of rotation.
Several known solutions to this problem have been proposed.
According to a first method, the cavity is offset at an angle in the mold such that, for example, the joint plane cuts the rectangular cross section of this cavity along one of its diagonals. Release from the mold by rotation of the jaws in the manner described hereinabove is then made possible. This solution is not satisfactory, however, for certain types of manufacturing. Thus the manufacture of hollow glassware products is frequently carried out in two main stages by means of I.S. (Individual Section) machines. During the first stage, the parison or glass glob is introduced into a preforming mold, the base of which is extended by a ring mold used for final shaping of the open upper part of the manufactured product.
The ring mold also has the function of gripping the preform in a subsequent operation in which the said preform is turned upside down prior to the second stage, in which the preforming mold is replaced by a finishing mold in which the hollow product is shaped by blowing.
Of course, the positioning of the preform in the preforming mold and thus the shape thereof must be adapted to correspond to the positioning of the internal cavity in the finishing mold. Despite such adaptation, when the said cavity is provided with the angular offset described hereinabove, homogeneous distribution of the glass in the cavity cannot be achieved. In fact, the zones of the parison close to the short sides of the rectangle are hotter than those close to the long sides, because they are surrounded by a smaller quantity of the material which constitutes the mold and which can remove heat from the glass. In addition, regular movement of glass close to the comers is impaired. Under these conditions, the specialists have observed that introduction of the preform into the finishing mold provided with an angular offset made it more difficult to obtain products with the desired symmetric shapes; instead, flattened zones or other distortions in relation to these shapes can be observed, especially at the comers. In certain cases, it may prove necessary to introduce into the finishing mold a more built-up preform, meaning one whose shape is closer to the final shape.
Furthermore, because of the inhomogeneity of temperatures and of distribution of the mass of the glass, it is almost impossible to make the lines corresponding to the joint plane of the preforming mold and of the finishing mold coincide on the product. On the contrary, the formation of two different lines for a given mold configuration cannot be prevented in controlled and reproducible manner; the appearance of the resulting product is affected thereby.
A variant of the first method comprising angular offset of the cavity as described herein is known by the name of "mold with broken joint plane". The disadvantages related to inhomogeneity of the glass mass are not eliminated with this variant. Moreover, this type ofjoint plane leaves larger marks on the finished product, for reasons that are not very clear at the present time; furthermore, molds of this type wear out particularly quickly.
According to a second method, attempts have therefore been made to dispense with angular offset of the cavity, which is blamed for production of dissymmetries on certain products obtained, while preventing the molded substance from being gripped by the mold at the moment of release from the mold, especially in the comers, as indicated hereinabove. To achieve this, the portion of the mold representing the cavity face most distant from the axis of opening of the mold could be made translationally movable. In such a configuration, however, it appeared difficult to avoid complex and cumbersome peripheral mechanisms, which would be subject to large torsional stresses and finally to rapid wear and excessively difficult disassembly and/or cleaning.
Consequently, the inventors achieved the present invention, which has as its object a mold with at least two jaws. More particularly, the invention is characterized by at least one element which can move rotationally relative to a first jaw, and by the fact that a portion of the surface of the said pivoting element constitutes a portion of the internal cavity of the mold when the mold is in closed position.
At the moment of release from the mold, therefore, the wall of the internal cavity which tends to grip the corners of the molded product is stripped progressively so that such gripping can no longer occur. Secondly, an arrangement of the internal cavity which is symmetric relative to the general shape of the mold and to its joint plane is not incompatible with the invention; the risk of formation of undesired dissymmetries is therefore minimal.
Preferably the mold comprises a means for closing the pivoting element of the invention, this closing means being provided with a bearing surface which acts on the pivoting element during closing of the mold. This bearing surface may belong to a part external to the mold jaws. However, it belongs advantageously to a second jaw itself or to another similar pivoting element mounted to move rotationally on such a second jaw.
As for the opening means, in relation to the first jaw, of said pivoting element which is mounted thereon, it preferentially applies a restoring force on said pivoting element. It is this restoring force which guarantees that the element will make contact with the said bearing surface of the aforesaid closing means during the terminal phase of closing of the mold and the initial phase of opening thereof. Of course, the restoring force is applied on a face of the pivoting element other than that capable of making contact with the closing means, opening and closing of the pivoting element corresponding to the two opposite directions of its freedom of rotation relative to the said first jaw. The means for application of the restoring force may be external to the mold jaws or alternatively may be installed in the said first jaw.
The pivoting element of the invention may also be translationally movable, especially in a direction substantially perpendicular to the portion or the wall of the internal cavity of the mold constituted by the said element. This variant makes it possible to achieve greater clearance of the element during release from the mold; in certain embodiments, however, it is appropriate to ensure that this advantage is greater than the aforesaid disadvantage of cumbersome, complex peripheral mechanisms subject to large mechanical stresses.
According to a particularly advantageous embodiment, the mold comprises two elements mounted on two different jaws which, in closed position of the mold, are joined to form a portion of the internal cavity free of visible discontinuity from one element to the other, except for the relatively thin mark of the lateral joint plane which they define. This variant is particularly effective when the portion in question of the internal cavity is a complex or faceted surface or a rounded surface bearing relief patterns which constitute just as many causes for gripping between the mold and the molded product during release from the mold.
According to the invention, each jaw is preferably provided with 0, 1 or 2 pivoting elements. In the case of a two-jaw mold, the mounting of a single element on one side of a single jaw will already achieve the expected result in the majority of cases.